Units that are given a charge order wait until their next attack order to charge. Once that happens they keep the charging Attribute for a time based on their courage, after which it should shut itself off. Likewise, there is a cooldown before a unit can charge again (shortened based on a unit's courage stat as well).

Hmm.. it may be coincidence, but i found after selecting charge, if i force them to Rifles and then tell them to choose their own weapon, that seems to stop the charging. But again, it may be just coincidence.